Collaborative Research: Forced drivers of trends in ocean biogeochemistry: Volcanos and atmospheric carbon dioxide

世界海洋在全球碳和氧循环中发挥着重要作用。除了在碳的自然循环中的重要性外，海洋还吸收了化石燃料燃烧排放的约40%的二氧化碳。了解导致海洋碳和氧浓度时空变化的过程对于预测这些海洋循环未来的发展至关重要。最近基于测量的估计和计算机模型都认为，海洋碳吸收在1990年代初大幅增加，然后在该十年的其余时间里放缓。观测和模型也显示了显著的氧气变化。这些模式的一个可能的驱动因素尚未被探索，是大型火山爆发的影响，特别是1991年的皮纳图博火山。随着火山爆发，小颗粒被迫上升到很高的高度，在那里它们通过高层大气传播，将阳光反射回太空，导致全球气候暂时变冷。该项目将探索这种暂时的冷却如何影响海洋环流，以及空气-海洋碳和氧交换，通过比较包括和不包括Mt的影响的地球系统模型模拟。皮纳图博火山爆发。在NCAR的社区地球系统模型大包围（CESM-LE）努力的框架内，该团队将完成一项新的实验，明确排除来自Mt. Pinatubo（CESM-LE-NoVolc）.通过与现有的CESM-LE（包括所有强迫）的不同，研究人员将直接确定Mt.皮纳图博，并把这些影响的背景下观察到的碳和氧的变化。具体而言，他们提出了两个假设：假设1：自20世纪90年代以来，地表通量和人为碳和氧的内部分布趋势受到了Mt.假设2：在最初的摄取异常，由于山。皮纳图博，温跃层异常，是凉爽的和有害的高示踪剂返回到表面。这些异常现象抑制了火山爆发后长达十年的空气到海洋的通量。最近的工作还表明，大气二氧化碳增长率的变化对海洋碳吸收的变化有一级影响。研究人员还将使用一个新的CESM海洋冰后报和CMIP 6模型的分层分析进行初步分析，以进一步探讨这一问题。具体来说，他们提出了第三个假设：假设3：通过在模拟中包括大气二氧化碳的季节循环和纬度分布，全球综合海气碳通量的变化性增加，并且变得更接近于基于观测的估计。通过创建CESM-LE-NoVolc，这项工作将允许调查Mt.皮纳图博对海洋地球化学和物理过程的广泛研究。模型运行将在CESM-LE项目伞下轻松提供。在这个研究项目下，研究生和本科生的研究将得到支持。该团队将继续我们长期以来的努力，以吸引未被充分代表的学生对科学，并解释海洋和碳循环科学向公众和K-12的学生。这个奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

The world’s oceans play an important role in the global carbon and oxygen cycles. In addition to their importance in the natural cycling of carbon, the oceans have absorbed approximately 40% of the carbon dioxide that has been emitted by fossil fuel burning. Understanding the processes that cause spatial and temporal variations of ocean carbon and oxygen concentrations is critical to predicting how these ocean cycles will develop into the future. Recent measurement-based estimates and computer models agree that ocean carbon uptake increased significantly in the early 1990s and then slowed over the rest of the decade. Observations and models also indicate significant oxygen variations. One possible driver of these patterns that has not been explored is the influence of large volcanic eruptions, specifically Mount Pinatubo in 1991. With the eruption, small particles were forced to great altitude where they spread through the upper atmosphere, reflected sunlight back to space, and led to a temporary cooling of global climate. This project will explore how this temporary cooling influenced ocean circulation, and air-sea carbon and oxygen exchange, by comparing Earth system model simulations that do and do not include the effects of Mt. Pinatubo’s eruption. Within the framework of NCAR’s Community Earth System Model Large Ensemble (CESM-LE) effort, the team will complete a new experiment that explicitly excludes forcing from Mt. Pinatubo (CESM-LE-NoVolc). By difference from the existing CESM-LE that includes all forcing, the investigators will directly identify the effects of Mt. Pinatubo and put these effects in context with observed carbon and oxygen change. Specifically, they propose to address two hypotheses: Hypothesis 1: Trends in surface fluxes and interior distributions of anthropogenic carbon and oxygen since the 1990s have been significantly impacted by Mt. Pinatubo.Hypothesis 2: After the initial uptake anomaly due to Mt. Pinatubo, thermocline anomalies that are cool and anomalously high in tracers return to the surface. These anomalies suppress air- to-sea fluxes for up to a decade after the eruption. Recent work has also indicated that variability in the growth rate of atmospheric carbon dioxide has a first-order effect on variability of ocean carbon uptake. The investigators will also do preliminary analysis using one new run of the CESM ocean-ice hindcast and a stratified analysis of CMIP6 models to further explore this issue. Specifically, they propose a third hypothesis: Hypothesis 3: By including the seasonal cycle and latitudinal distribution of atmospheric carbon dioxide in simulations, variability of the globally integrated air-sea carbon flux is increased and becomes more comparable to observationally-based estimates. By creating CESM-LE-NoVolc, this work will allow for investigation of the forced impact of Mt. Pinatubo on a wide range of ocean biogeochemical and physical processes. Model runs will be made easily available under the CESM-LE project umbrella. Under this research project, graduate and undergraduate research will be supported. The team will continue to our long-standing efforts to attract underrepresented students to science, and to explain ocean and carbon cycle science to the general public and K-12 students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.